In order to remove nitrogen oxides from the exhaust gasses of combustion engines, reducing agents such as liquefied urea is often introduced into the exhaust systems. This is typically done by use of a nozzle that ensures atomization of the reducing agent. However, the introduction of reducing agents often results in deposits in the form of crystals or amorphous structures building up in the nozzles used to deliver the reducing agent or in the exhaust pipes and/or on surfaces of the exhaust system. These deposits grow in size over time and thereby result in a poorer atomization and a poorer control of the delivered amount. They must therefore be removed from time to time which requires dismantling of parts of the system.
In accordance with the present invention, it has been realized that formation of deposits often occurs in regions of the exhaust system where recirculation regions are present. Formation of deposits may also occur where so-called initiating points are present, which initiating points are regions of a wall into which the atomized reducing agent flows towards and contacts and where depositing is initiated and grows out from. Initiating points are often burrs, cams, projections, knobs, high spots or the like.
Hence, an improved system and method for removal of nitrogen oxides from exhaust gasses without build-up of deposit would be advantageous.